Dual Reconstructions of Iron Phosphates/Molybdates on Nickel Foams with Disparate Dynamics for Oxygen Evolution Reaction.

For NiFe-based precatalysts, there is a general consensus that they will undergo reconstruction to generate NiFe (oxy)hydroxides as real active sites during the electrochemical oxygen evolution reaction (OER), but the current understanding of the reconstruction process is still far from satisfactory. Herein, iron phosphates/molybdates on nickel foams (FPmM/NF, m = 5, 7, 10, 20) were prepared via a coprecipitation method, where although both MoO42- and PO43- undergo anion exchange during the activation process, i.e., dual reconstructions, to form NiFe (oxy)hydroxides, they show disparate reconstruction dynamics. By tuning the phosphates/molybdates ratio, the morphology, activity, and activation rate of the formed NiFe (oxy)hydroxides can be tuned. Consequently, the obtained optimal FP7M/NF-activated (FP7M/NF-a) possesses a fast and deep reconstruction with a morphology of nanoparticles with a disordered structure and rich oxygen vacancies, thus exhibiting exceptional OER activity (overpotentials of only 175 and 180 mV at 50 and 100 mA·cm-2) and excellent stability.